2G2 PRESIDENTIAL ADDRESS. 



tion did not chance to occur ; the question is whether use- 

 inheritance has increased the percentage of these particular 

 variations. And it is a question on which, as it seems to me, 

 it is exceedingly hard to obtain satisfactory evidence one way 

 or the other. 



Those who are disposed to regard use-inheritance as a 

 factor in evolution have generally laid stress on the fact that 

 it is the effects of persistent use or disuse through a series of 

 generations that are effectual in giving a permanent set to 

 the species. I am surprised, therefore, that Mr. Ball should 

 attempt to show that use-inheritance, if it existed, would be 

 detrimental to the species. It is surely self-evident that 

 use-inheritance as a source of origin of variations would be 

 beneficial to the species. According to Mr. Ball, adaptation 

 is the result of the selection of favourable variations ; use- 

 inheritance, if it occurs, would provide an increased per- 

 centage of these favourable variations, and not leave the 

 matter to chance. Surely this would be a clear gain. This, 

 however, is no valid argument for its occurrence, unless we 

 are prepared to take the questionable ground sometimes 

 occupied by extreme selectionists, and say. Variations of all 

 kinds are constantly occurring ; a variation in the direction 

 of use-inheritance would be beneficial ; natural selection 

 fosters and develops beneficial variations ; therefore natural 

 selection has developed use-inheritance. Grant the possi- 

 bility of use-inheritance and this reasoning may hold good ; 

 but the whole question at present is as to the actual occur- 

 rence of use-inheritance or not. What we really want is evi- 

 dence which, through the elimination of disturbing factors, 

 shall point definitely in one direction or the other. 



We have seen that the American school of biologists con- 

 tend that variations, for example in tooth-structure, are 

 determinate and not indeterminate. They also contend that 



